This competitive renewal application is designed to obtain extended follow-up of a unique cohort of asymptomatic patients with rotator cuff tears from which substantial and encouraging data has been obtained. The broad aim of this proposed research is to determine the natural history of rotator cuff disease and factors important in the clinical deterioration of tears. This information is fundamental for determining proper surgical indications and optimizing outcome. These patients offer a rare opportunity to determine risk factors for tear degeneration over time as treatment intervention has not been necessitated by the onset of symptoms. Additionally, we aim to establish two new follow-up cohorts which should provide important adjunctive information regarding partial-thickness tear progression and the relationship between the development of fatty degeneration with tear size, tear location and the development of new pain. Our specific aims are as follows: Specific Aim 1: To obtain long-term follow-up of full-thickness tears to evaluate factors important for tear deterioration and symptom development. A population of 89 individuals identified as having unilateral asymptomatic rotator cuff tears have been followed for minimum period of 2 yrs. Important information regarding alteration in glenohumeral kinematics, rate of tear enlargement, changes in muscle strength and fatty degeneration are anticipated with longer-term follow-up. These patients will be followed with yearly radiographic, outcome, ultrasound and clinical exams for up to 10 yrs. Specific Aim 2: To determine the probability of partial tear progression to full-thickness tears. For 48 individuals previously enrolled with partial-thickness rotator cuff tears and 50 new recruitment patients, yearly high resolution ultrasound exams will be performed to determine the risk of complete tear degeneration. Specific Aim 3: To longitudinally follow full-thickness tears to determine factors important to the development of fatty degeneration. Fatty degeneration of rotator cuff muscles is an irreversible phenomenon associated with decreased healing and outcome following surgical treatment. Ultrasound will be employed to assess what factors such as tear location, tear size, and patient age may be important in the development of fatty degeneration. To date, data from the enrolled population of patients with asymptomatic rotator cuff tears have provided a wealth of new information regarding the natural history of cuff disease and important factors for surgical indications. The proposed project could be an important next step in understanding the natural history of cuff disease and innovative in that a unique study population of asymptomatic tears and partial tears will be longitudinally followed during an extended time of symptom development and tear deterioration with fatty degeneration. With the proposed study design, risk factors for irreversible tendon or muscle deterioration will be studied. This knowledge is important to determine the necessity for early operative treatment.